Project Summary Despite the prevalence of female reproductive pathologies, such as endometriosis and ectopic pregnancy, there is shockingly little known about the molecular or cell biology of the organs involved. This proposal focuses on the oviduct, because the oviduct serves as the conduit between the ovary and uterus, and is the site of mammalian fertilization. While the oviduct is a critical site for female fertility, how oviduct physiology is regulated at the genetic, molecular, and cellular level is almost completely unknown. Like all female reproductive organs, the oviduct undergoes recurrent tissue morphogenesis in response to the cyclical hormonal changes of the estrous cycle, which is the fundamental hormonal regulator that allows all mammals, including humans, to become pregnant. The oviduct is lined by a single layer of epithelium which is composed of multiciliated and secretory cells. The multiciliated cells (MCCs) project hundreds of motile cilia from their apical surface, where they beat together and are hypothesized to capture the ovulated oocyte and sweep it down the oviduct. The MCCs remodel dramatically during the estrous cycle: during the first half of the cycle, the percentage of MCCs increases and peaks at ovulation, after which the percentage of MCCs decreases significantly. While oviduct epithelial remodeling is known to occur, it is completely unclear how these remodeling events are regulated. Does oviduct MCC remodeling occur via apoptosis or deciliation? Do stem cells participate in these remodeling events? In multiciliated tissues, cilia beat together because the tissue is planar polarized. How is planar cell polarity of the oviduct lost and regained throughout the estrous cycle? Finally, how are these remodeling events regulated at the genetic level? This proposal seeks to explore oviduct MCC remodeling using a combination of mouse genetics, high resolution imaging of cell shapes and behaviors, in vivo imaging of oviduct fluid flow, and unbiased genomic analysis. The work proposed here will provide new insights into the turnover of oviduct multiciliated cells and the genomic control of oviduct epithelial homeostasis (Aim 1), and the establishment of planar cell polarity in the oviduct (Aim 2) during the estrous cycle. Understanding the genetic, molecular, and cellular basis of MCC remodeling of the oviduct during the estrous cycle holds therapeutic promise for treating female infertility and improving the success rates of in vitro fertilization.